The ability to detect the presence of compounds in samples is extremely important in commerce and everyday life. The field of analytical chemistry has thus seen continuous development in this area. Although various methods have been developed that allow for the detection of various target species in samples taken from sources such as the environment, a continuing need remains for devices and methods for detecting such compounds.
While certain methods have been developed for the detection of organoamines and organophosphorus compounds, a need remains for methods which do not require expensive instrumentation and which are both convenient and easy to use. Organophosphorus compounds such as organophosphonates are known to destroy nerve impulse transmissions between nerve fibers, muscles, and glands within mammals and insects. Therefore, these compounds have been utilized as nerve agents for chemical warfare and as pesticides in commercial agricultural applications. The toxicity of many of these materials, as measured by the LD50 value, from inhalation into the lungs of the most common such chemical warfare agents is around 200 ppbv. Furthermore, organophosphonates may be delivered through a variety of routes including by absorption through the skin, by injection into a vein, by injection under the skin, and by oral delivery. The exposure criteria for many pesticides and insecticides is less clear because a wide variety of organophosphonates have been synthesized. Conventionally, exposure of agricultural workers to organophosphonates is conducted using body fluids because measurements of vapor concentrations of these materials remains difficult. Therefore, occupational monitoring of these compounds has focused on measuring the enzymatic activity of cholinesterase in blood samples, by analyzing metabolite byproducts in urine samples, and by analyzing saliva or perspiration.
Past studies for detecting organophosphonates have employed a wide range of coating materials and schemes for transducing physical changes in the states of the coatings. These schemes include: optical techniques that use fiber-optic micromirrors and waveguides; electrical resistivity methods; mass-sensitive methods such as quartz crystal microbalances and surface acoustic wave devices; cantilever sensors that deflect upon absorption of analyte; lanthanide ions that luminesce upon coordination of the organophosphonate with the copolymer; and surface analytical techniques such as infrared spectroscopy. M. A. Butler, A. J. Ricco, Anal. Chem., 1992, 64, 1851; J. F. Giuliani, N. L. Jarvis, A. Snow, ACS Symposium Series No. 309., 1986, 320; M. Eldefrawi, K. Rogers, A. Eldefrawi, Pesticides and the Future: Toxicological Studies of Risks and Benefits, Reviews in Pesticides Toxicology 1, edited by Hodgson, E., Roe, R. M., Motoyama, N., Department of Toxicology, University of North Carolina, Raleigh, 1991; E. S. Kolesar Jr., R. M. Walser, Anal. Chem., 1988, 60, 1731; E. S. Kolesar Jr., R. M. Walser, Anal. Chem., 1988, 60, 1737; S. W. Oh, Y. H. Kim, D. J. Yoo, S. M. Oh, S. J. Park, Sensors Actuat B., 1993, 13–14, 400; O. S. Milanko, S. A. Milinkovic, L. V. Rajakovic, Anal. Chim. Acta., 1992, 269, 289; W. P. Carey, B. R. Kowalski, Anal. Chem., 1986, 50, 3077; M. S. Nieuwenhuizen, J. L. N. Hartveld, Sensors Actuat B., 1994, 18–19, 502; M. S. Nieuwenhuizen, J. L. N. Hartveld, Talanta., 1994, 41, 461; J. W. Grate, S. N. Kaganove, S. J. Patrash, R. Craig, M. Bliss, Chem. Mater., 1997, 9, 1201; L. Bertilsson, K. Potje-Kamloth, H.-D. Liess, B. Leidberg, Langmuir 1999, 15, 1128; G. Li, L. W. Burggraf, Appl. Phys. Lett., 2000, 76, 1122; A. L. Jenkins, O. M. Uy, G. M. Murray, Anal. Comm., 1997, 34, 221; and A. L. Jenkins, O. M. Uy, G. M. Murray, G. M. Anal. Chem., 1999, 71, 373.
The detection of biogenic amines is important because these compounds are markers of the freshness of foods such as fish and meat. Common biogenic amines such as histamine, putrescine, and cadaverine are produced by the microbial decarboxylation of the amino acids histidine, ornithine, and lysine, respectively. In order to provide a fresh and safe food supply, governments such as the United States have placed maximum limits for these materials in foods. A convenient and simple method for detecting these compounds is thus an important problem that has not yet been resolved.
Past studies of the binding of low molecular weight compounds such as amines to receptors hosted on surfaces have employed one of three general transduction schemes; optical techniques that utilize fluorescence, chemiluminescence or waveguide/surface plasmon resonance; electrical methods utilizing potentiometric, amperometric, and conductive techniques; and mass-sensitive methods such as quartz crystal microbalance and surface acoustic wave devices. T. M. Swager, Acc. Chem. Res., 1998, 31, 201; E. Delamarche, A. Bernard, H. Schmid, B Michel, J. A. Biebuyck, Science, 1997, 276, 779; E. V. Groman, J. M. Rothenberg, E. A. Bayer, M. Wichek, Methods Enzymol., 1990, 184, 208–217; L. Yang, S. S. Saavedra Anal. Chem., 1995, 67, 1307; L. S. Jung, C. T. Campbel, T. M. Chinowsky, M. N. Mar, S. S. Yee, Langmuir, 1998, 14, 5636; R. P. Buck, E. Lindner, Acc. Chem. Res., 1998, 31, 257; M. Niculescu, C. Nistor, I. Frébort, P. Pe , B. Mattiasson, E Csöregi, Anal. Chem., 2000, 72, 1591; J. Wang, Q. Chen, C. L. Renschler, C. White, Anal. Chem., 1994, 66: 1988; H. Bayley, C. R. Martin, Chem. Rev., 2000, 100, 2575; C Barnes, C. D'Silva, J. P. Jones, T. J. Lewis, Sensors and Actuators A, 1992, 31, 159; M. Rodahl, F. Hoeoek, B. Kasemo, Anal. Chem., 1996, 68, 2219; S. Yao, K. Chen, D. Liu, L. Nie, Anal. Chim. Acta., 1994, 294, 311; J. W. Grate, Chem. Rev., 2000, 100, 2627; and S. J. Martin, G. C. Frye, S. D. Senturia, Anal. Chem., 1994, 66, 2201.
Although many of the conventional assay methods work well in detecting the presence of target species, most conventional assay methods are expensive and often require instrumentation and highly trained individuals, which makes them difficult to use routinely in the field. For example, the detection of analytes using fluorescence or chemiluminescence techniques requires the use of labels while electrical, mass-sensitive, and surface plasmon techniques require complex instrumentation. Thus, a continuing need exists for assay devices and systems which are easier to use, which do not require complex instrumentation, and which allow for evaluation of samples in remote locations where quick results may be required.
Recently, assay devices that employ liquid crystals have been disclosed. For example, a liquid crystal assay device using mixed self-assembled monolayers (SAMs) containing octanethiol and biotin supported on an anisotropic gold film obliquely deposited on glass has recently been reported. Gupta, V. K.; Skaife, J. J.; Dubrovsky, T. B., Abbott N. L. Science, 279, (1998), pp. 2077–2079. In addition, PCT publication WO 99/63329 published on Dec. 9, 1999, discloses assay devices using SAMs attached to a substrate and liquid crystal layer that is anchored by the SAM.
Although various methods have been used to detect the presence of a compound in a sample, a continuing unmet need exists for a simple device and method that may be used to rapidly detect the presence of a compound in liquid or gaseous samples. A continuing need also remains for a method of manufacturing a device for use in detecting the presence of compounds in a sample.